Simple lithium grease and lithium complex grease are well known greases in the art. They are the most common type of greases in use and have widespread industrial utility and a good multi-purpose versatility. It has been estimated that lithium greases account for about half of the total grease market.
Currently, an issue in the market for grease is the demand for greases with better performance than simple lithium greases. Attributes of grease performance particularly sought are improvements in mechanical and thermal stability. This demand for higher performance is currently met by lithium complex greases, see for example U.S. Pat. No. 4,410,435; Naka et al.
Lithium complex greases possess many of the properties of simple lithium soap greases and also have higher dropping points, allowing the greases to be used at higher temperatures. The dropping point of lithium complex greases is higher than that of simple lithium soap greases due to the presence of a second thickener component, known as a complexing agent. Modern lithium complex greases typically use a shorter chain-length difunctional carboxylic acid, such as azelaic acid or adipic acid. The lithium salt of these materials is typically present in a significantly lower proportion compared to the simple lithium soap thickener. An alternate material used as a complexing agent is boric acid. The use of this material also results in an elevated dropping point.
Due to their improved performance properties, Lithium complex greases can be significantly more expensive to produce that simple lithium greases. Therefore, there is currently a need for lithium grease of performance intermediate to that of a simple lithium grease and a lithium complex grease.